Sky Dome and Vray Skylight Problem?

[Donald2B]

Okay, I have a strange problem that I have a work around for, but I don't know if there is a more elegant way to approach this problem. So here it goes.

All of the exterior renders that I do, use a skydome (Squashed sphere with the bottom sliced off, normals flipped to the interior, image mapped accordingly). With standard Max lights, using a light dome I didn't have this problem. Now that I am updating some of these scenes using VRay I have encountered this problem. The skydome seems to be blocking the skylight of VRay. Is there a way to have the skydome NOT included in the GI calculations but STILL be used for reflections?

My current solution is to turn off Receive Reflections/Refractions on the objects properties. Render out an IR map, and then reenable Recieve Reflections/Refractions and render using the save IR map. This does an okay job and is pretty painless. The only problem with this is that my render times go up dramatically when I start adding reflective objects in my scene. It is as it has to recalculate the GI when it gets to a car or large areas of glass.

Does this make sense? If anyone could help point me in the right direction I would really appreciate this! I am trying to refrain from rendering seperate passes and comping them in later due to the short period of turn around time that I have to get these exteriors done. Any and all help would be greatly appreciated. Thanks all!!

~Troy

[Da_elf]

ive never personally tried using a skydome. i just put my environment in the environment slot.

[Donald2B]

The main reason is for an animation.

What method do you use for putting the sky in the enviroment slot? Just curious.

Thanks!

~Troy

[Da_elf]

simply put a 360 spherical image into the environment slot as a spherical mapped environment image

[michaelinitaly]

How do you adjust the placing of the image when it is in the enviroment slot?

I have been using a dome and mapping a image to it and then turning the dome to get it to have the image in the correct place. I have not had any problem getting the sun blockec by the dome, but the dome was not receiving light so I put in a large vray light and only have it effect the skydome.

The problem I have is shooting a animantion through the dome. I have tried everything I can think of to let me shoot through it. I have only one sided material..in the end I have to either slice the dome or make the dome bigger.

Michael

[RErender]

It just takes a little instancing to control the map in the environment:

1. Make a standard material with your background map in the diffuse slot.

2. Drag the map from the ME to the environment map slot and choose "instance".

3. In the "Viewport Background" roll-out check "use environment background".

Now you should see the map as it will render. adjust the offset and tiling in the material you created and it will update in the viewport . You may want to apply the material to a non-renderable box or something in case it gets covered in the ME.

[Geddart]

hey Donald2B

You encountered a bug - vlado knows about it.
I had the same Problem when doing my Griesgram Animation. I ended up rendering the Background with Scanline in a separate Layer.
Skydome has it's reasons for existance - you have much better control over the image directly in the viewport.
I also encountered something that was only working with a Skydome - can't remember what it was though.

[suitaloon]

All of the exterior renders that I do, use a skydome (Squashed sphere with the bottom sliced off, normals flipped to the interior, image mapped accordingly). With standard Max lights, using a light dome I didn't have this problem. Now that I am updating some of these scenes using VRay I have encountered this problem. The skydome seems to be blocking the skylight of VRay. Is there a way to have the skydome NOT included in the GI calculations but STILL be used for reflections?

have you tried to turn off the cast shadow button on the properties menu of the object?

[Da_elf]

actually guys its not a bug. Its a simple principle that goes back a long time to when mental ray first came out for max. primary bounces and secondary bounces. GI is a secondary bounce and that includes GI from your vray environment light. However. also linked to secondary bounce is reflection and refractions. So if you try to tell it not to block out the skylight your also tellng it not to reflect refract. You talk about having something in your viewport to easily control. I see it also as something in your viewport to get in the way of clearly seeing my scene. My ME is always open in the other screen so reaching over there and playing with a peramiter to rotate my sky isnt so tough. I know everyone has their own methods though and it would be nice if a way was found to exclude an object from blocking GI yet still reflecting and refracting in other objects.

ps. a shadow cast by a light source is a primary bounce effect. therefore turning that off doesnt affect an object blocking GI light from the skylight

[suitaloon]

ps. a shadow cast by a light source is a primary bounce effect. therefore turning that off doesnt affect an object blocking GI light from the skylight

Thanks for the tip da_elf...

[Donald2B]

After running MANY tests this weekend, I have come to the conclusion that an environment map is NOT going to work for me. I don't have enough control over the map and as soon as I use this method in an animation, the results are NOT desirable.

I do have many different work arounds that I have been using, so it just takes me a couple of extra steps to get to a final output. Eagerly awaiting the latest update for VRay.

Thanks for all of the great discussion!!

~Troy

[conceptdesign]

Render heory

The best way I have found to get around this is to calculate the IR map with incrimentaly add and save it for the animation with the skydone turned off - Then use the ir map you have just calculated and turn on the skydome - seems to work just fine

Mike

[Donald2B]

Conceptdesign: Yes, this does work and has been one of my many workarounds. The only problem with this is that it takes longer to render once you turn the skydome back on. It is as though any object with reflections takes MUCH longer to render.

So I have been using Da_Elf's advice and just removed my skydome and used a gradient ramp environment material for the sky. It doesn't look AS good, but my rendertimes have dropped significantly, 2 minutes a frame difference over a 3500 frame animation is a BIG deal.

[Da_elf]

there is one major flaw to that technique concept design
if your using interpolated glossies they will be recalculated when your using your saved incremental added map. The problem with this is they are recalculating what would be reflecting in them in the situation with the skylight dome put in. therefore your reflections will be of objects without skylight since the dome blocks it. I realised this when i was trying to do a scene where i used white colors in a scene to calculate irradiance map then added the colors so i could have a scene without color bleeding. however i had a glossy floor with interpolated glossies. and the walls in the scene were blue and the roof white. in my reflections on the floor the roof had blue color bleeding on it since the newly calculated glossy reflections were of that point in time where the colors had been added back in. Only work around for that is the longer render time of having non-interpolated glossies.

[Donald2B]

Okay, I definitely see what you are saying! That makes total sense. Thanks for the great explanation!

~Troy